Hey SunnyDays,
I assume you are talking about the plastic washers? You only need all 8 of them if you are installing on a 115X socket without the optional backplate.
If you indeed are using socket 115X without the backplate, the correct washer is M4 PA (ad 9mm id 4,3mm x 0,8). You can check if your local hardware store has any, or we can send you a replacement (washer for free, but you would have to carry shipping 3,45€).

Is there a customized HEATKILLER water block for my...GPU | Motherboard

Hey SunnyDays,
I assume you are talking about the plastic washers? You only need all 8 of them if you are installing on a 115X socket without the optional backplate.
If you indeed are using socket 115X without the backplate, the correct washer is M4 PA (ad 9mm id 4,3mm x 0,8). You can check if your local hardware store has any, or we can send you a replacement (washer for free, but you would have to carry shipping 3,45€).